In the field of digital data storage systems, five and one-quarter inch Winchester disk drives are widely used, and their dimensions have been standardized at 3.25 inches by 5.75 inches by 8.0 inches. The storage capacity of these units has been increasing, with the 1500 series units made by Micropolis, the assignee of the present invention, now having a storage capacity above 350 megabytes; and it is expected that this capacity will at least double in the relatively near future. Incidentally, a "byte" of digital information includes eight binary digits or "bits" of information, a megabyte is a million bytes or 8,000,000 bits, and one gigabyte is a billion bytes or eight billion (8,000,000,000) bits of digital information.
With the relatively high production quantities of five and one-quarter inch Winchester disk drives, the cost per megabyte has come down to a moderate level. However, for higher storage capacities, coupled with higher data rates, typically accomplished by 101/2 and 14 inch parallel head Winchester drives, the cost per megabyte has been substantially higher, in the order of at least two or three times the cost per megabyte of the individual five and one-fourth inch drives.
Accordingly, a principal object of the present invention is to provide a large scale, high data rate storage system having a substantially lower cost per megabyte than the systems which are currently available.
Incidentally, proposals have been made heretofore to use two or more Winchester type drives together, to provide higher reliability or a larger storage capacity. For example, reference is made to U.S. Patent Defensive Publication No. T932,005 dated Mar. 4, 1975, U.S. Pat. No. 3,623,014, granted Nov. 23, 1971 and to European Patent Application Nos. 85 4004 93.4 published Oct. 2, 1985, 156,724. The first two references cited above essentially use a second Winchester drive to duplicate the stored information, to provide increased reliability. Concerning the European Patent Publication, it appears to include a superficial disclosure of a system in which it is proposed that several Winchester drive storage units be employed, and in which successive bits of incoming data are to be routed to the different storage units. It is also noted that the various Winchester drive units are not synchronized, thereby adding additional delays to data access times.
As compared with the foregoing prior art arrangements, principal objects of the present invention are to reduce the data access time, and to provide a reliable, high capacity, high data rate, and relatively inexpensive storage system.